In conventional air conditioners, a large-capacity compressor has been used for rapid heating in which warm air is supplied to the room in a short time. However, a large-capacity compressor has a low reliability of liquid back, and the temperature of the large-capacity compressor rises at each operation start requiring a large amount of heat energy, so that the efficiency of rapid heating is low. Liquid bag is a phenomenon in which a liquid refrigerant, not gaseous refrigerant, is sucked into a compressor due to insufficient evaporation of the refrigerant when the evaporation temperature is lowered below freezing temperature during heating operation.
An air conditioner disclosed in Japanese Patent Publication No. 2009-085484 controls a four-way valve at every startup to communicate an outlet port of the compressor and an inlet port of the compressor, thereby reintroducing the refrigerant discharged from the compressor to the compressor. With this configuration, the refrigerant temperature may be raised within a short time after every startup without using a large capacity compressor.
However, since the refrigerant does not flow into an indoor heat exchanger or an outdoor heat exchanger while raising the temperature of the refrigerant of the compressor in conventional air conditioners, it is difficult to realize rapid heating or rapid defrosting proportional to a rate of raising temperature of the refrigerant.